JPS5896456A - Picture element density controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for writing matrix data using constant amplitude write pulses.
The present invention relates to a device for controlling gray scale or print density in a printer. More specifically, the present invention provides for varying the total writing time, in which constant amplitude pulses are applied to the printing electrodes for one complete writing cycle, as a function of the desired density of the pixel to be printed. The present invention relates to a matrix printer controller for controlling the gray scale of charge sensitive media.

In all non-innocent printers that use electrically sensitive media, printing can be accomplished by applying a sufficient voltage to the printer's writing stylus for a predetermined period of time. The "writing" ability of an electrically sensitive recording medium depends primarily on the amplitude and/or the voltage pulse applied to the printing stylus force, i.e. the electrode.
or is a function of duration. All known printers of this type rely solely on amplitude changes to print.

This is because changes in the relative difference between the speed of movement of the recording medium and the speed of completion of the write cycle, including the writing start and end points of the pixels during the write cycle, will affect the print quality unless compensated for. This is because alignment errors that have an adverse effect will occur. The compensation described above is more expensive than using write pulse root width control (see margin below) and requires significantly lowering or stopping the speed of the recording medium during the write cycle.

Without this alignment problem and performance degradation due to compensation, the time-varying method allows the use of fully saturated devices and avoids the need to use variable drive voltages for the write electrodes. Therefore, it will be widely used. The time-varying method provides high operating efficiency, low power consumption, and reduced heat generation and dissipation.

It is known in the art to use constant amplitude time-varying pulses. A circuit utilizing this is shown in US Pat. No. 3,441,946. This circuit also provides a write signal to a single-needle recorder using electrically sensitive paper. More specifically, the write control circuit is arranged to vary the frequency of the write pulses as a function of the speed at which the recording medium is driven under the printing stylus. Thus, different recording conditions and speeds can be compensated for and the extent to which the media is printed can be controlled. Another conventional printer is disclosed in U.S. Pat. No. 3,553,718 in which time-based control of write electrodes is used.

In this patent, constant amplitude current pulses are applied successively to a plurality of writing needles, the duration of which is proportional to the signal to be recorded such that the shading of the recording indicates the amplitude of the signal.

US Pat. No. 3'613103 discloses an electrolytic recording device in which the analog signal to be recorded is converted into a series of rising pulses spaced apart in inverse proportion to the amplitude of the signal. This control circuit generates a series of pulses that
The pulse generator is configured for use in triggering the pulse generator.

The output of this pulse generator is a series of constant amplitude writes with a spatial density proportional to the original signal amplitude. More specifically, a configuration is disclosed in which a large number of juxtaposed write electrodes are energized sequentially.To effect continuous operation of the write electrodes, a time division demultiplexer converts the time division signals into The control circuit of this patent is configured such that the write electrodes are energized for one pulse during each one clock period.

These prior art write electrode control devices do not operate satisfactorily and are not suitable for use when the recording medium is moved in the printer and multiple electrodes are used during the actual printing operation. isn't it.

That is, prior art control systems either produce unacceptable print registration errors or do not work with current matrices that move electrosensitive recording media at a constant speed.
Unable to adapt to printer requirements.

The object of the present invention is to move a recording medium by
, Kusu! The purpose of the present invention is to provide an attempt to control gray scale generation without causing unacceptable print registration errors in a printer.

Another object of the invention is to provide a gray scale control system for a matrix printer that reduces the maximum allowable registration error to a very small extent.

Another object of the present invention is to provide a gray scale control system that generates P print density levels while using hardware and encoding that is fully compatible with modern integrated chip technology.

Another object of the present invention is to provide a gray scale control device which requires only one power supply to obtain the write electrode drive voltage and which requires only a fully saturated device to generate said drive voltage. Our goal is to provide the following.

According to the invention, A with equal amplitude and duration loop 1
Means is provided for issuing a predetermined number of concentration clock signals having different internal on-times during the duration.

The number of density clock signals generated is equal to the number of bits forming the code word for the required printable density level. The on-time l of each clock signal is selected to be a collection of several subdivision times of the printer's write cycle. Each clock signal uses a different predetermined combination of such subdivision times.

The clock signal encodes density level information for each write electrode to generate a write pulse waveform that drives the electrodes to form pixels whose start and end points are substantially equal regardless of the density being printed. is logically combined with Printing pixels of different densities] 7 The resulting pixel size differences are forced to occur in the center of the pixel, and are less likely to occur at the end of the pixel. By generating a write pulse waveform in which the on-time difference at the endpoint is only one subdivision time, the endpoint difference and tolerance error is at most one write cycle subdivision time. limited.

In the following description, unless otherwise specified, the words "writing" and "printing" are used to have the same meaning. Similarly, the words ``electrode'' and ``needle'' have the same meaning,
The terms "write pulse II, II print pulse" and "print voltage" are also used interchangeably. Furthermore, "write cycle time" refers to the time required to write, i.e., the time to supply the write electrodes to print one row of pixels across one width of the recording medium in use. means,
Ru.

In matrix printers of the type described above, the recording medium is constantly moved at a predetermined speed and the typical write cycle time is 500 microseconds or 0.5 milliseconds (ms). This is the amount of force required to energize each of the multiple write electrodes that are mounted across the recording medium and encompass all or part of the width of the print head ready for the next write cycle. It's time. The typical speed of movement of the recording medium is 1
It is constant at 12.7 (5 inches) per second. Assuming that one particular electrode remains in use for the entire write cycle time to obtain maximum print density, that electrode will have a pixel length of 0.0635 mm (0.0025 inch) at that recording media speed. is printed.

When the pixel density is to be lower, the appropriate write electrode is activated for a shorter time. In other words, the print pixel density is a function of the time that the drive voltage is applied to the print electrodes. The length of the printed pixel is a function of the speed at which the recording medium moves relative to the write electrode and the printing time.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a 0.50 ms basic write cycle 20 that is subdivided into a number of equal width sections 1 to 10.
S indicates the start point of the write cycle 20, and E indicates the end point of the write cycle 20. The number of write cycle subdivision times or portions that must be formed depends on the maximum allowable alignment error as well as the number of density levels required (although this is of minor concern).
is a function of In this example, the write cycle is divided into 10 equal parts of 0.05m5 each.

Therefore, if the recording media speed is 12.80 crn/sec (5 in/sec), the maximum alignment deviation in pixel length for each write cycle subdivision time of the on time is 0.80 crn/sec (5 in/sec).
It is 00635 mm (0,00025 inches).

Generally speaking, under normal conditions and without compensation, the maximum alignment error that will occur for one write cycle subdivision time is a function of the number of write cycle subdivision times.

In one conventional method of gray scale control,
It is simply necessary to turn on the write electrode for a portion of the write cycle as long as necessary to produce a pixel of the desired density at the beginning of each write cycle. It's just that. Thus, as illustrated in FIG. 2, pixel 22 is printed by driving the associated write electrode during the first three subdivision times of write cycle 20. Accordingly, the pixel 22 is formed under the conditions described above to have a long portion 22a of 0.01905 mm (0.00075 inches) and a core portion 22b. The length of the core portion 22b is a function of the diameter of the associated write electrode. The higher density pixel 24 has a long portion 24a with a length of 0.001'50 inches and a core portion 24b whose length is a function of the associated write electrode diameter. Generated by printing for six write cycle subdivision times. length is 0.057
A higher density pixel 26 having a long portion 26a of 15 mm (0,00225 inches) and a core portion 26b whose length is a function of the diameter of its associated write electrode is used for the first nine write cycles. Printing is performed by applying a pulse to the associated write electrode during the subdivision time. In addition, in FIG. 2, S indicates the starting point.

The longitudinal misregistration between pixels 22, 24 and 26 is noticeable in matrix printers of the type described above, with printed electrode diameters of 0.0127 cm (0, [
] This is particularly noticeable in the typical case of 0.05 inches).

When using such conventional methods, the difference in pixel length is most noticeable when the end or start points of pixels are at the same location and the brightest and darkest pixels are printed adjacent to each other. Therefore, if all pixels have the same starting or ending points that draw attention to a common point of reference, some compensation is necessary to avoid visually discernable alignment errors as described above. It is desirable to solve the registration error problem by having the majority of the electrode write cycle drive waveforms and the pixels of different densities printed by them begin and end at the same location or point of reference.

For this reason, in an embodiment of the invention, the concentration clock pulse generator 28 is connected to the oscillator 3, as shown in FIG.
0. Binary counter 32, decoder 34, reset circuit 3
6 and logic circuit 58 to provide a predetermined number of concentration and lock pulses. The number of intensity clock pulses provided is equal to the number of bits of encoded information required in the code word to uniquely determine the number of available intensity levels (four in the example). In this example, the binary counter 32 and the decoder 34 are
It is constructed using chips 5N74193 and 5N54154 of Trument Corp., but it can also be constructed using other integrated circuit chips having similar functions. Furthermore, instead of a binary counter and decoder, a decimal counter and a decoder suitable for this cuff can be used. It will also be apparent to those skilled in the art that the concentration clock pulse generator can be constructed using discrete circuitry.

(First, in response to the start signal on the input line 40, the reset circuit 3614 binary counter 62 is set to zero and begins its counting operation. The counter 32 receives the output signal 42 of the oscillator 30. The individual pulses of the signal 420 are It has the same period as the subdivision time of the write cycle 20. The five complete pulses of the output signal 42 of the oscillator 30 are equal in length to the basic write cycle 20. The pulse amplitude of the pulse train 42 depends on the particular logic used. The outputs of binary counter 62, lines 32aX32b, 32c and 32d, are each connected to the input of decoder 34.

Counter output line 32a carries a value of 1 containing a pulse train having a frequency that is half the frequency of counter input pulses 42. Counter output line 32b has a value of 2, which includes a pulse train having a frequency 1/4 of the frequency of counter input pulses 42.

Similarly, the counter output line 32c is connected to the counter input pulse 4.
4 containing a pulse train having a frequency 1/8 of the frequency of 2
It has the value . Counter output line 32d has a value of 8, which includes a pulse train having a frequency 1/16 of the frequency of counter input pulse 42.

Decoder 34 decodes these signals by acting on the energization states of the input lines and produces a number of individual pulse outputs on sixteen output lines 34a through 34p. For example, the output line 34a is
It starts at position subdivision time 1 of write cycle 2o and consists of a single subdivision pulse with the same duration. Output line 34bH consists of one pulse signal having the same position and duration as subdivision time 2 of basic write cycle 20.

Similarly, output lines 34c-34j consist of pulse signals having the same positions and durations as subdivision times 6-10 of write cycle 20, respectively. In this example, 10
If only one write cycle subdivision time is selected, no further decoder outputs are required. Decoder output line 34 outputs the tenth or final subdivision time of write cycle 20 to restart counter 62 after the required ten signals are obtained from decoder 34.
A reset line 46 is connected between j and the reset circuit 66. When the last subdivision pulse occurs on line 54j, reset circuit 66 is activated, which resets counter 62 and begins generating subdivision pulses again. The remaining six output lines of decoder '54 are not used.

The output signal of the decoder 34 is supplied to a logic circuit 38,
Here they are logically combined to form density clock pulses A, B, C and D to be generated on logic circuit output lines 38a through 58d, respectively. As shown in FIG. 4, the density clock pulses A through have waveforms of the same overall duration and amplitude as the basic write pulses 20. The important difference is that they are each "on" only for different predetermined portions of the same total duration. The density clock pulse A is supplied to the output line 38a by, for example, taking the logical sum of the decoder output lines 34a and 34j in the logic circuit 38 from the subdivision time 1 pulse and the subdivision time 10 pulses. The positive portions of density clock pulse A, subdivision times 1 and 10 are each equal to the write cycle subdivision time. A density clock pulse B containing only subdivision pulses 2.6 and 1Q is obtained by discharging into logic circuit 58 and disjuncting decoder output lines 54b, 54c and 34j. , concentration clock pulse B
and the positive portions of subdivision times 2.3 and 10 are each equal to the width of the write cycle subdivision time. Concentration clock pulse C (l'' is subdivided into pulses 4, 5, 6 and 10 only, and in logic circuit 38, decoder output line 34d
, 34e, 34f and 4j. Concentration clock pulse C and subdivision time 4
．． The forward portions of 5.6 and 10 are each equal to the write cycle subdivision time. The density clock pulse DIfi is configured to include only subdivision pulses 7 to 10, and is obtained by the logical sum of decoder output lines 34g to 34j in the logic circuit 38. The density clock pulse D and the positive portion of subdivision times 7 to 10 are each equal to the width of the write cycle subdivision time.

The number of density levels that determine grayscale resolution can be chosen arbitrarily, but is eleven in the preferred embodiment. This choice is independent of the number of write cycle subdivision times, but can be the same. The number of subdivision times selected is a function of the smallest tolerable error, and the number of density levels is a function of the hardware and coding required to represent each density level uniquely. Using four numbers, up to 16 unique combinations or intensity levels can be encoded into a multi-bit word. However, it is also possible to select a smaller number of density levels, such as using only 11 density levels as in this example. As previously mentioned, the number of bits selected to simultaneously encode the desired density level determines the number of density clock pulses required. The greater the number of code words required to define the concentration levels and the greater the amount of hardware required to decode and generate write electrode waveforms that support more concentration levels and The cost will increase.

By "effective on-time" is meant the total time that drive voltage is applied to a particular printing stylus during an acceptable write pulse occurrence.

Density clock pulses A, BXC, and D are used alone or in combination to generate write pulse waveforms 48 for each of the 11 desired print density levels with one exception. Ru. Write pulse waveforms 48a-48 are shown in FIG. Intensity level identifiers are shown to the left of each of waveforms 48a-48. The codes for these waveforms are shown on the right along with the effective on-time. The first density level obtained using write pulse waveform 48a'z is generated without using a density clock pulse and corresponds to the above exception. The second density level is obtained using a write pulse waveform 48bi consisting of clock pulse A only. Similarly, the third density level is obtained by using the write pulse waveform 48c' (H) consisting only of the clock pulse B.The remaining density level waveforms are as follows:
Concentration clock pulse A as reflected by clock code
, R, C and D are combined. For example, the seventh density level is obtained by logically combining density level clock pulses A, B, and D'.

Only write pulse waveforms 2.5.6 and 9 do not start at the same point like the remaining write pulse waveforms. However, on each side, these four waveforms lag the other waveforms by one write cycle subdivision time.

Therefore, the actual maximum alignment error at the starting point of the four write pulse waveforms is the recording medium speed (12
, 7α/sec (5 inches/sec)) and the subdivision time (005 microseconds), which is 0.0635 mm (0,0
025 inches). The maximum time between subdivision pulses in the write pulse waveform is the time indicated by write pulse waveform 1, which is also the waveform for clock pulse A.

This waveform has eight consecutive subdivision times in the off state. The pixel formed by this is 0.0508
It has a beginning and an end separated by a gap having a length of mm (0, OD 2 inches). However, since the gap occurs at the center of the pixel, the pixel appears complete and uniform to the observer. Note that the human eye tends to perceive pixels with an open center as complete much more easily than pixels with uniform differences in start or end points. As a result, the only discernible alignment errors are due to differences in the beginning of the write pulse waveform 48, which in this embodiment of the invention amounts to no more than one band of cycle subdivision times. becomes.

FIG. 6 shows a portion of a circuit 50 that generates write pulse waveforms 48a-48k. Since the entire circuit 50 functions in the same manner as portions of the circuit not shown, the following description of portions of the circuit is sufficient to understand the operation of the entire circuit. In the particular portion illustrated, the write pulse waveform 48e for the fifth concentration level is obtained by the drive circuit 52 for the first write electrode, and the write pulse waveform 48h for the eighth concentration level is obtained by the drive circuit 52 for the first write electrode. It is assumed that this is obtained by the drive circuit 54 for the two-layer electrode. The serial data is encoded to indicate the concentration level required for each write electrode.
Shift register 56 is input via input line 58 .

When activated, shift register 56 transfers its contents to inter-office buffer 62 in parallel under control of clock line 60.

The first stage of buffer 62 includes a clock code (1a01)'r for the fifth concentration level;
The clock code for the eighth density level (11 o
1) Includes e. The output of the intermediate nozzle 62 is multiple AND
Gate 64 (AND gates 64a, 64b in FIG. 6)
, 64 c, 64 d, 64 e, 64 f,
64g and 64h are shown). The other inputs of each of AND game) 64a to 64h are the density clock pulse AXB.

It is connected to receive one of C and D. A set of four AND gates 64 are each connected to receive one of the concentration clock pulses and are connected to an OR gate 66, as described below. Specifically, in the illustrated portion of the 7 circuit 500, the AND gate 6
4a to 64d are connected to receive density clock pulses A to all, respectively, and to provide a human logic operation result to an i0R gate 66& to generate a write pulse waveform 48e for the fifth density level; AND gates 64e to 64h are configured to receive concentration clock pulses A to all, respectively, and write pulse waveform 4 for the eighth concentration level.
In order to generate 8h'e, the input logical operation result is connected to be supplied to the QOR gate 66b.

The AND gate 64a receives the density clock pulse A and also receives the logic HI times signal from the buffer 62. AND
Gates 64b and 64c receive density clock pulses B and C, respectively, at one of their inputs, but are inhibited by a logic LO times signal provided from buffer 62. ANDK) 64d receives the concentration clock pulse D? at one of its inputs. buffer 6 on the other input.
2 from logic I (I signal). As a result, AND gates 64a and 64d are held on by the code in buffer 62 and write pulse 48e for the combination of density clock pulses A and D, i.e., the fifth density level. It is output to the OR gate 66a and the drive circuit 52.Similarly, the AN
D gates 64e, 64f, and 64h output density clock pulses A and 64h, respectively, based on the contents of second stage buffer 62.
Only B and D are applied to the 'ffOR gate 66b. As shown in FIG. 5, the combination of density clock pulses AXB and D is the write pulse 48h for the eighth density level.
This write pulse is applied to the write electrode drive circuit 54 from the OR gate 66b. The two pixels printed in this way will have different center gaps due to the difference in the write pulse waveform and the effective on-time between the two subdivision times, but to the human eye they are cannot be distinguished. Therefore, long pixels generated by using the present invention all appear to be the same length. Alignment errors occur in only four instances, but this is limited to an absolute minimum of one write cycle subdivision time.

Although the above description is for a printing environment where the recording medium is continuously moving, it is of course that the present invention is also useful for matrix printers where the recording medium is paused during the print cycle. It will be obvious to business owners.

[Brief explanation of the drawing]

FIG. 1 is an illustration showing an example of a basic write time cycle according to the present invention for a matrix printer using an electrically sensitive recording medium moving at a constant speed; FIG. An illustration showing the six basic write time cycles with pixels superimposed to show the alignment errors that occur when FIG. 4 is a block diagram illustrating an example of a logic circuit according to the present invention used to generate the density clock signal used to derive the waveform of the write pulse waveform that energizes the print electrode. A timing diagram showing the four different density clock signals used to generate the entire subdivision time. Figure 5 shows the relationship between the write pulse waveform used to obtain a particular density dot and the density of the printed dot. , a clock code and a timing diagram showing the effective on-time for each available write pulse waveform and density level. FIG. 2 is a block diagram illustrating an example of a portion of a circuit according to the invention used to obtain an image; 5 Cl-0-1 oscillator, 32...binary counter,
34...decoder, 36...υ set circuit, 5
8...Logic circuit, 56...Shift register, 6
2...Intermediate buffer, 64 a, 64 b, 6
4 c, 64 d. 64e, 64f, 64g, 64h-AND gate,
66a, 66b=”OR gate.

Claims (1)

Claims: In a matrix printer having a plurality of printed electrodes and a drive circuit for the electrodes, a charge sensitive recording medium to be printed by the electrodes during a write cycle having a predetermined number of equal subdivision times. Apparatus for controlling the density of a pixel, comprising: a storage device for receiving and storing encoded multi-bit words indicative of pixel density data; each density clock pulse signal being associated with and different from a separate bit of the multi-bits; a first circuit for generating a number of equal density clock pulse signals of equal amplitude equal to the number of bits of the coded word, including a number of write cycle subdivision pulses; and the storage circuit connected to the first circuit to receive the density clock pulse signal and to receive the encoded word to generate a write pulse waveform in response to the density clock pulse signal. a second circuit connected to the drive circuit and connected to the drive circuit;